Method for thermally regenerating the heat exchanger material of a regenerative post-combustion device

ABSTRACT

In order to regenerate the heat exchanger material located in the various segments of a housing section ( 2 ) of a regenerative post-combustion device ( 1 ), air is heated in the combustion chamber ( 8 ) of this post-combustion device ( 1 ) by a burner ( 9 ), is directly removed from the combustion chamber ( 8 ), is adjusted to the desired regeneration air temperature using fresh air, and is returned to the inlet ( 4 ) of the thermal post-combustion device ( 1 ). The outlet ( 10 ) of the thermal post-combustion device ( 1 ) remains closed during this operation. The rotary distributor ( 5 ) of the thermal post-combustion device ( 1 ) rotates during this process which is continued until all segments of the heat exchanger material are heated to a temperature at which the contaminants absorbed by the heat exchanger materials are released and combusted in the combustion chamber ( 8 ).

The invention relates to a method for thermally regenerating the heatexchanger material of a regenerative post-combustion device, which in ahousing comprises from top to bottom:

a) a combustion chamber;

b) a section, which is divided into several segments filled with heatexchanger material;

c) a rotary distributor having a direction of rotation, which accordingto its rotary position produces:

ca) a connection between an inlet for a waste gas to be purified and afirst segment of the heat exchanger material;

cb) a connection between a second segment of the heat exchanger materialand an outlet for the purified gas;

cc) a connection between the third segment of the heat exchangermaterial, which segment is ahead of the second segment in the directionof rotation of the rotary distributor, and an inlet or an outlet forflushing gas;

in which method air is heated in the combustion chamber, is removed fromthis, adjusted to the desired regeneration air temperature using freshair, and is routed successively through all segments of the heatexchanger material, due to which the heat exchanger material is broughtto a temperature at which contaminants adsorbed by the heat exchangermaterial are released.

Regenerative post-combustion devices are used to purify contaminatedwaste gases from industrial processes. To conserve energy on thermalpost-combustion, the waste gases to be purified are led through heatexchanger material. Since the waste gases to be purified often containorganic contaminants in the form of condensable substances, e.g. tarproducts, or organic dust, the surfaces of these heat exchangermaterials become clogged with these contaminants in the course ofoperation. To regenerate it, the heat exchanger material has to beheated periodically to a temperature at which the contaminants absorbedby the surface are released and can be removed. This takes place inknown thermal post-combustion devices in that fresh air is introducedinto the combustion chamber, heated there to high temperature and thenconducted from the top downwards through the heat exchanger material,routed via the rotary distributor to the outlet and then removed to theoutside atmosphere via the chimney. The rotary distributor is stationaryin this process. It is waited until the segment of the heat exchangermaterial flushed through in each case has been heated from top to bottomto the required temperature, so that all areas of the heat exchangermaterial in this segment are freed of contaminants. The rotarydistributor is then rotated by one segment, and the process commencesafresh. What is disadvantageous about this known method for regeneratingheat exchanger material is on the one hand the relatively long timerequired to clean all segments. In addition, the gas routed to thechimney contains the contaminants released from the heat exchangermaterial, and is thus not clean.

The object of the present invention is to configure a method of the typespecified at the beginning so that thermal regeneration takes placequickly and in addition no contaminants are released into the ambientatmosphere.

This object is achieved according to the invention in that the air usedfor thermal regeneration and heated in the combustion chamber is removedfrom the combustion chamber and returned to the inlet for waste gas tobe purified, while the outlet for purified gas is closed, and this airis circulated with the rotary distributor rotating until all the heatexchanger material has been sufficiently heated and all contaminantshave been released from this.

Due to the recirculation of the heated air to the inlet providedaccording to the invention, two things are achieved:

On the one hand, the segment of heat exchanger material acted upon ineach case is heated from underneath, i.e. from a side which is normallyrelatively cool, as it is far removed from the combustion chamber.Uniform heating of the heat exchanger material in the segment can thusbe achieved more quickly than if this segment was acted upon with hotair from the combustion chamber. On the other hand, in the processaccording to the invention, the air which carries the contaminantsreleased from the heat exchanger material is introduced into thecombustion chamber, where these contaminants are combusted and thusrendered harmless. Thus only air which is completely free ofcontaminants is released into the environment via the chimney.

One practical example of the invention is explained in greater detailbelow with reference to the drawing; the single FIGURE showsdiagrammatically a regenerative post-combustion device with theprincipal peripheral devices required for its operation.

The regenerative post-combustion device is identified in the drawing bythe reference symbol 1. Its basic structure and its basic mode offunctioning are—unless otherwise stated—described in EP 0 548 630 A1 orEP 0 719 984 A2, to which express reference is made.

In the lower area of the housing 2 of the regenerative post-combustiondevice 1 is an inlet chamber 3 for the waste gas to be purified, whichis supplied via an inlet line 4. Depending on its rotary position, arotary distributor 5 arranged in the inlet chamber 3 produces aconnection between the inlet chamber 3 and a segment from a number ofsegments in the shape of cake slices in a distribution chamber 6 locatedabove the inlet chamber 3. Located above the distribution chamber 6 inthe housing 2 is a heat exchange chamber 7, which is divided into acorresponding number of segments, which each communicate with acorresponding segment of the distribution chamber lying underneath. Thesegments of the heat exchange chamber 7 are filled with heat exchangermaterial.

Located above the heat exchange chamber 7 in the top area of the housing2 is a combustion chamber 8, into which a burner 9 discharges.

The rotary distributor 5 is formed in a known manner such that itconnects a further segment of the distribution chamber 6, which isgenerally diametrically opposed to the first-named segment, and thusalso a further segment of the heat exchanger chamber 7 to an outlet line10 for purified gas. Finally, the rotary distributor 5 produces aconnection between that segment of the distribution chamber 6 and thusof the heat exchange chamber 7, which segment is ahead when seen in thedirection of rotation of the rotary distributor 5 of the segment whichcommunicates with the outlet line 10, to a flushing air line 11.

The outlet line 10 for purified gas leads via a motor-controlled valve12 and a fan 13, a further motor-controlled valve 14 and a soundabsorber 15 to a chimney 16. Branching off between the fan 13 and themotor-controlled valve 14 is a return line 17, which is connected via afurther motor-controlled valve 18 to the inlet line 4 for waste gas tobe purified. The flushing air line 11 already mentioned, in which afurther motor-controlled valve 19 lies, branches off the return line 17.Also opening into the flushing air line 11 between the valve 19 and theinlet to the regenerative post-combustion device 1 is a fresh air line20 connected to the outside atmosphere, which line is closable by afurther motor-controlled valve 21.

Finally, the combustion chamber 8 is connected to the outlet line 10 forpurified gases at a point between the motor-controlled valve 12 and thefan 13; this connection can be opened or closed by a motor-controlledvalve 23 opening into the line 22 between the motor-controlled valve 23and the point of discharge into the outlet line 10 is a fresh air supplyline 24, which can likewise be closed by a motor-controlled valve 25.

Normal operation of the regenerative post-combustion device 1, in whichcontaminated waste gases are treated, corresponds to the known process:

The waste gas 4 to be purified is introduced into the inlet chamber 3 ofthe regenerative post-combustion device 1 via the inlet line 4 and isconveyed onwards to a certain segment of the distribution chamber 6according to the respective rotary position of the rotary distributor 5.The waste air rises from this segment of the distribution chamber 6 intothe segment of the heat exchange chamber 7 lying above it and takes upheat stored previously from the heat exchanger material there. The wastegas is heated on passing through the heat exchanger material, until onemerging from the top side of the heat exchange chamber 7 it has eitherreached the ignition temperature for the contaminants contained in it,or is approaching this ignition temperature. In the latter case,combustion of the contaminants is carried out with the aid of the burner9; in the former case, combustion takes place without the supply ofexternal energy.

The heated air, now containing the (harmless) combustion products,enters a segment of the heat exchange chamber 7 from above and flowsdownwards through this. In doing so it gives off a large part of itsheat to the heat exchanger material there and on the underside of theheat exchange chamber 7, suitably cooled, it enters the correspondingsegment of the distribution chamber 6 and is routed by the rotarydistributor 5 to the outlet line 10. In this operating mode, themotor-controlled valves 12 and 14 are open and the motor-controlledvalves 18, 23 and 25 are closed. The clean air is removed with the aidof the fan 13 via the chimney 16 to the outside atmosphere.

As already mentioned above, the segment of the heat exchange chamber 7which is ahead in the direction of rotation of the rotary distributor 5of the segment through which the clean air passes is flushed withflushing air. In the practical example shown, this flushing takes placesomewhat differently to the case in the publications mentioned above:here, clean air is supplied, namely via the return line 17 and theflushing air line 11, with the motor-controlled valve 19 open and themotor-controlled valve 21 closed, via the rotary distributor 5 to theappropriate segment of the heat exchange chamber 7. This difference inthe nature of the flushing, however, is insignificant for the basic modeof operation of the thermal post-combustion device 1, at any rate in thepresent connection.

Following a fairly long period of operation, the heat exchanger materiallocated in the heat exchange chamber 7 requires regeneration, as itssurfaces have become clogged by substances, for example tar products ororganic dust carried by the waste gas to be purified. This thermalregeneration takes place in the regenerative post-combustion device 1described as follows:

The supply of waste gas to be purified via the inlet line 4 is stopped.The motor-controlled valves 12 and 19 are closed, whereas themotor-controlled valves 14, 18, 21, 23 and 25 are opened.

In this switching state of the various motor-controlled valves, hot airis removed from the combustion chamber 8. Fresh air is admixed via thefresh air supply line 20 and the regeneration air temperature setthereby. The mixed air is taken in using the fan 13 via the line 22 andthe open valve 23 and supplied via the return line 17 and the openmotor-controlled valve 18 to the inlet line 4 and from there via theinlet chamber 3, the rotary distributor 5 and the corresponding segmentof the distribution chamber 6 to a segment of the heat exchange chamber7. This air enters the combustion chamber 8 upwards again and is heatedby the burner 9. The hot air is circulated on the route described, whilethe rotary distributor 5 continues to rotate. Surplus air in the circuitis removed by suitable opening of the motor-controlled valve 14 to thechimney 16.

The air circulation described is carried out with the rotary distributor5 running until the heat exchanger material even in the lowest areas hasreached the temperature at which the deposits are removed from the heatexchanger material. These contaminants are then brought by thecirculating air to the combustion chamber 8 and combusted there. Oncethis process is complete, the various motor-controlled valves are resetto the starting position once again and the supply of waste air to bepurified via the inlet line 4 is resumed.

What is claimed is:
 1. A method for thermally regenerating a heatexchanger material of a regenerative post-combustion device, which in ahousing comprises from top to bottom: a) a combustion chamber; b) asection, which is divided into several segments filled with heatexchanger material; c) a rotary distributor having a direction ofrotation, which according to its rotary position produces: ca) aconnection between an inlet for a waste gas to be purified and at leastone corresponding first segment of the heat exchanger material; cb) aconnection between at least one corresponding second segment of the heatexchanger material and an outlet for the purified gas; cc) a connectionbetween at least one corresponding third segment of the heat exchangermaterial, which segment is ahead of the corresponding second segment inthe direction of rotation of the rotary distributor, and one of an inletand an outlet for flushing gas, the method comprising the steps ofheating air in the combustion chamber, removing the heated air from thecombustion chamber, adjusting the removed air to a desired regenerationair temperature using fresh air, conducting the temperature-adjustedremoved air successively through all segments of the heat exchangermaterial, bringing the heat exchanger material to a temperature at whichcontaminants adsorbed by the heat exchanger material are released,removing the air used for thermal regeneration from the combustionchamber, returning the air to the inlet for the waste gas to bepurified, while the outlet for purified gas is closed, and circulatingthe air with the rotary distributor rotating until all the heatexchanger material has been sufficiently heated and all contaminantshave been released from the heat exchanger material.